1. Field of the Invention
The subject invention relates to instruments for measuring the characteristics of fluids, and more particularly, to an improved instrument and method for testing the color, turbidity and/or fluorescence of fluids such as water mixed with a reactant.
2. Background of the Related Art
Water quality monitoring at all levels of production and usage is rapidly becoming a global necessity as sources of fresh potable water become taxed by increasing populations. Even low levels of foreign matter or contaminants can pose significant health and safety risks when undetected. As a result, fast and accurate water testing results are required of an ever-expanding source of test samples. Consequently, there is a growing need for rugged portable instruments and methods for monitoring water quality as the treatment and usage of water expands.
Typically, the testing of water quality has involved the addition of a specified reagent to a fluid sample. Conventionally, a reactant of known concentration is mixed with a water sample which contains a reactant of an unknown concentration. Alternatively, the known reactant is continually added until a sample property change indicates the endpoint of the reaction. In either case, the reagent reacts with the contaminant to create a reaction proportionate to the concentration of the contaminant. Often, a color indicator is included so that a color change occurs, or the color change is inherent to the chemical reaction. Thus, subsequent to the addition of the reagent, visual inspection against a printed color chart can determine the absence or level of an associated contaminant. Such purely visual comparisons are inherently subjective, and therefore unreliable for sensitive measurements. Generally, a skilled technician is required to determine the degree of the reaction and interpret the results. Alternatively, a colorimeter or photometer can consistently measure the degree of reaction (e.g., the depth of color or the spectral transmission) and, hence, the concentration of the contaminant. However, traditional calorimeters and photometers are not practical for field use and provide only color related data.
When the reaction product is a fine-particle precipitate, the sample can be measured by optical turbidimetric methods, i.e. scattering. A high concentration of precipitate as a result of a high concentration of the contaminant creates increased scattering. Therefore, the level of turbidity corresponds to the level of contaminant concentration. Alternatively, the presence or absence of a level of turbidity from a source in a natural fluid sample may be a critical indicator of the quality of such a fluid sample.
An additional technique is to add a reagent including a fluorescent marker. The reaction with the contaminant may either enable or quench the fluorescent moiety. For example, the marker rhodamine will fluoresce in the red when excited by blue light. Thus, transmitting blue light through the sample will generate a red fluorescence proportionate to the level of contaminant. Accordingly, determining the change in the level of fluorescence will indicate the concentration of the contaminant. Additionally, if the blue exciting light is repetitively pulsed and the fluorescence intensity is measured at a particular time after each pulse, the time-decay rate of the fluorescence can provide further information on the chemical nature of the contaminant.
In view of the above, several systems have been developed to ascertain the color, turbidity or fluorescence of a liquid sample. A traditional calorimeter includes a broadband light source. Filters are moved in and out of the optical path to provide different wavelengths. The filters may be moved manually or by motors. A lightpipe or lens system may collect and direct the light to a point on the object to be tested. At such points, the light reflects off opaque objects and passes through translucent objects to receivers. The receivers, usually photodiodes, convert the light signal into an electrical signal for processing. To prevent erroneous readings, the receiver must be isolated from ambient light. To control the environment, the conventional colorimeter is usually utilized exclusively in a laboratory.
For example, U.S. Pat. No. 5,137,364 to McCarthy discloses an optical spectral analysis device having light emitting diodes (hereinafter xe2x80x9cLEDsxe2x80x9d) and receivers mounted on the same substrate. Thus, only reflected light is analyzed. U.S. Pat. No. 5,229,841 to Taranowski et al. shows using a plurality of different colored LEDs which are run according to timing pulses. In synchronism with the LED timing pulses, the outputs of the photodiodes are sampled, and thus each output is indicative of an individual colored LED""s signal. U.S. Pat. No. 6,094,272 to Okamoto discloses receiving a sum total of reflected light and comparing the summed value to a value associated with a reference target. The resulting comparison value is displayed in numerical form to indicate a match degree between the tested item and the reference item. U.S. Pat. No. 6,157,454 to Wagner et al. discloses a miniature calorimeter. The miniature colorimeter includes a body having a light pipe for transmitting reflected light to a light sensor, three different primary colored light sources, a display panel and a measure button. In operation, the miniature colorimeter generates three color data points representing the reflectance of the target measured at the wavelengths of the three primary colors. A microprocessor analyzes the three data points and displays the results in various commonly known formats. Further, several patents are directed specifically to water testing methods and devices. U.S. Pat. No. 5,618,495 to Mount et al. automates the process of determining when the endpoint of the reagent reaction is reached with the use of a computer in communication with a colorimeter and other devices. U.S. Pat. No. 5,691,701 to Wohlstein et al. uses the voltages generated by photosensors to produce a ratio which indicates the condition of engine oil. If the test fluid is outside a preset acceptable limit, an alarm indicating the same is triggered.
A multitude of patents are directed to particular aspects of photoelectrically sensing the color of an object. For example, U.S. Pat. No. 5,303,037 to Taranowski discloses a color sensor illumination source which generates a white light evenly composed of red light, green light and blue light directed at the same angle. The importance of a balanced source is to yield relatively balanced color output readings. U.S. Pat. No. 5,471,052 to Ryczek shows a secondary photosensitive element which receives the light directly from the light source. As a result, the signal from the secondary photosensitive element is used to create a closed loop feedback signal to regulate the light source power output.
Additional patents have recognized that certain materials display different colors depending upon the angle of observation. In particular, U.S. Pat. No. 5,592,294 to Ota et al. recognizes the need to accurately determine the angle of observation in order to render reproducible results. To solve this problem, Ota et al. incorporated an angle detector which controls an adjustment mechanism in order to set the desired angle of observation repeatably.
U.S. Pat. No. 5,083,868 to Anderson discloses the need for a portable colorimeter. The colorimeter is enclosed in a housing for receiving a sample. When a vial is placed in the sample compartment, a cap member is positioned in grooves to prevent interference from external light. U.S. Pat. No. 5,872,361 to Paoli et al. discloses a portable turbidimeter having a non-imaging optical concentrator between a sample cell and an optical detector. A cover is utilized to reduce the effect of ambient light on the readings. U.S. Pat. No. 5,604,590 to Cooper et al. discloses a nephelometer instrument for measuring very high water turbidities, such as 10,000 NTUs. The nephelometer instrument has one light source and four detectors. The detectors receive back scatter, forward scatter, 90xc2x0 scatter and transmitted light.
Still further, several patents are directed to devices for only determining the light penetrability of liquids. U.S. Pat. No. 5,696,592 to Kuan teaches immersing a light guide and a liquid-tight photosensor in a liquid to be measured. When a light source illuminates the light guide, the photosensor generates a signal indicative of the penetrability of light for the test liquid. U.S. Pat. No. 6,055,052 to Lilienfeld is directed to a system for monitoring airborne particulates. Lilienfeld appreciates the need for a portable instrument which can determine ambient air quality in real time at remote locations. Each of the U.S. patents described above are incorporated herein by reference.
Despite the teachings of the above-mentioned patents, there are various problems associated with the systems and methods of the prior art as known in the field of water testing. Many systems require the time-consuming process of acquiring a sample and sending the sample to a laboratory for analysis. Alternatively, on-site analysis is often subjected to inconsistent results due to human error. Further, devices of the prior art, particularly those designed for portable field use, yield only limited results. In the past, providing a device that could consistently and accurately indicate contaminant levels was far less than economic regardless of the location. There is a need, therefore, for an improved water testing instrument and method which permits efficient and accurate readings of at least one, and preferably a plurality of parameters for a variety of applications and operating conditions.
The present invention is directed to a method and device for optically measuring qualities of a substance in ambient light, wherein the device includes a translucent wall defining a sample chamber and an axis. The translucent wall contains the substance to be measured. A radiation source, such as an LED or other light source, is mounted adjacent to the sample chamber and emits a modulated beam of radiation distinguishable from the ambient light because the radiation is modulated. After passage through the sample chamber, the radiation is received by a detector angularly spaced about the axis of the sample chamber relative to the radiation source. The detector generates a modulated output signal indicative of the intensity of the radiation of the beam impinging thereon. A controller activates the radiation source and the detector and processes the modulated output signal for show on a display.
The present invention is also directed to an instrument and method for measuring characteristics of a substance, wherein the instrument includes a sample chamber for receiving therein a sample of the substance. A signal generator has a radiation source mounted adjacent to the sample chamber. The radiation source emits a beam of radiation through the sample chamber onto a detector of the signal generator angularly spaced about the axis of the sample chamber relative to the radiation source. The detector receives the beam of radiation after passage through the sample chamber and substance to be measured therein. Upon receiving the radiation, the detector generates an output signal indicative of the intensity of the radiation impinging thereon. A memory stores reference measurement data based upon a plurality of different reference samples, wherein each reference sample has a different concentration of an impurity. A controller in communication with the memory is operative to receive a signal from the signal generator based upon a sample within the sample chamber having an unknown concentration of an impurity. The controller automatically compares the signal to the reference measurements to determine a concentration of the impurity in the sample and generate an output signal indicative of the concentration.
The present invention is also directed to a method and device for analyzing color and scattering of an elongated sample, such as a water sample contained in a vial, wherein the elongated sample defines an axis. The device includes a first channel defining a first meridional plane having a first radiation source mounted adjacent to the sample. The first radiation source emits a first beam of radiation through the sample onto a first sensor angularly spaced about the axis of the sample relative to the first radiation source. The first sensor generates a first output signal indicative of the intensity of radiation impinging thereon. A second channel defines a second meridional plane and includes thereon a second radiation source mounted adjacent to the sample. The second radiation source also emits a beam of radiation through the sample onto a second sensor angularly spaced about the axis of the sample relative to the second radiation source for generating a second output signal. Electronics activate each of the channels and process the signals generated thereby. Preferably, the channels are about 45xc2x0 apart to allow for color, transmission and 45xc2x0 turbidity measurements.
One advantage of the instrument and method of the present invention, is that they employ light sources which are modulated, and therefore the signals generated thereby can be isolated. As a result, the instrument and method are capable of functioning in ambient light. Further, multivariate analysis can be conducted simultaneously to gather data faster than with traditional mechanisms.
Still another advantage of the subject invention is the simplified arrangement of stationary components which perform a multitude of measurements. As a result, the reliability is improved and production costs are reduced.
These and other unique features and advantages of the instrument and method disclosed herein will become more readily apparent from the following description, the accompanying drawings and the appended claims.